In recent years, it has become possible to collectively read a number of RFID tags located at a long distance of 10 m or more from an antenna instantly using a radio frequency identification (RFID) technique of a UHF band. A readable distance is expected to increase further from now on due to an improvement in the performance of a RFID tag chip and the like.
The RFID tags have been increasingly used for many purposes such as high-speed reception and shipment checking in warehouses, stores, or the like, theft detection, and register settlement of products. However, there is a problem in that RFID tags other an originally intended reading target such as RFID tags attached to products displayed around an antenna are read, and thus there is a need for a technique capable of identifying only an RFID tag that has actually moved in front of an antenna.
In this regard, known is a technique in which a data generating means for associating reception information from an RFID tag with chronological information and generating a plurality of sets of a scan angle of a scan antenna at which the reception information is received and chronological information is provided, and a linear approximate straight line representing a relation between the scan angle and the chronological information is obtained using data generated by the data generating means, and a moving direction of a moving object with an RFID tag is detected based on the slope of the linear approximate straight line, or a moving locus of the moving object is obtained, and a moving direction of the moving object with the RFID tag is detected (Patent Document 1).
Further, known is a technique of calculating the distance between a reflective object and a distance measuring device with a high degree of accuracy through a distance measuring device that performs a process of receiving reflective signals transmitted from a reflective object through a plurality of different carrier frequencies and includes a distance calculating unit that analyzes the reflective signals transmitted from the reflective object and calculates the distance between the reflective object and the distance measuring device (Patent Document 2).
Further, known is a technique using a special antenna in which an antenna is arranged obliquely other than horizontally to a moving direction of an RFID tag or a direction of an output radio wave is skewed (Patent Document 3).
Patent Document 1: JP 2007-303935 A
Patent Document 2: JP 2009-80133 A
Patent Document 3: U.S. Pat. No. 7,817,014 B2 (FIG. 17a, and FIGS. 18a to 18b)